Although it is well-known that elements such as heating tubes, or other elements having cord profiles, can be soldered onto holding plates or heat transmitting plates, these methods involve a considerable consumption of labor. In addition, they can be applied only when specific metals or alloys are used for the jacket of the heating tube element or for the cord profile element, as well as for the heat transmitting plate. Furthermore, there is a danger that the components of the heating tubes may be damaged by the heat which develops during the soldering process, or that the materials of these structures may be affected in other detrimental ways.
It is also well-known that during the installation of the heating elements for appliances such as coffee percolators or the like, a tubular heating element, which has been bent in the shape of a horseshoe, and a water pipe have to be attached to each other by a suitable cold binding method to each other and then, subsequently, to a holding plate. In order to accomplish this, flanges are stamped out of the holding plate, which then are used to hold the series of profiles presented by the heating elements and the water pipes.
Furthermore, the German Pat. No. 2,336,149, laid open for inspection, gives a method of masked joining of relatively hard parts made of metal with relatiely soft parts made of metal. In this method, before the two metallic parts are pressed together, a metallic anchor element in the form of a wire spiral is soldered onto the hard metallic parts. The hardness of the material of this anchor element is higher than that of the soft metallic parts and lower than, or equal to, the hardness of the hard metallic parts.
When the joints of the kind described above involving materials with unequal thermal coefficients of expansion are exposed to multiple cycles of substantial temperature changes, as is typically the case with heating appliances, the joint very often deteriorates or cracks and the integrity of the joint is subsequently affected. This problem is further complicated by the requirement to maintain a maximum surface contact between the heater and plate surface, as well as the requirement to provide a constantly acting elastic force on the heating tube so that an even transmission of heat may be achieved. At present, this problem could be solved only partly because in the above-given example of the stamped-out holders, which are bent around the heating element and pressed onto it, the flanges stretch as time goes by and consequently fail to provide the corresponding constant heavy pressure which could ensure the corresponding transmission of heat.
Consequently, it is an object of the invention to provide a method of joining together substantially long elements with each other and with a metal plate, such as a heat transmitting plate or a similarly shaped element made of metal, which will both result in a reliable joint at minimum expense and will guarantee a uniform heating operation of the appliance for a reasonable length of time.
Also, to the extent that wire-shaped joining elements are used according to the presently known techniques, for example the method presented in German Pat. No. 2,336,149, these joining elements were used exclusively for rigid mechanical fastening together of the parts. However, they did not provide any elastic pressure, namely such elastic pressure which would be evenly applied over the entire length of the tube or of the track-like element and which would apply continuous pressure independent of variations in the diameter of the tube, which are unavoidable in tubular heating elements.